JPH0115521B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a process for the polymerization of chloroprene as well as the polychloroprene obtained by this process and its use in adhesive mixtures, but more particularly in aqueous emulsions in the presence of chain transfer agents. The purpose is a method for polymerizing chloroprene. Polychloroprene is frequently used in adhesives in the form of latexes and solutions in solvents. For this purpose, polymers are used in sol form, that is to say polymers soluble in solvents whose viscosities can vary. However, in order to obtain an adhesive characterized by high cohesive strength, it is desirable to have a certain viscosity. For most applications as adhesives, the polymer is masticated prior to dissolving it.
need to be operated. The purpose of mastication is to break the long networked or branched chains in the polymer that are responsible for the elastic behavior of the product. This operation is relatively expensive. There was therefore an interest in discovering a polymerization process which would make it possible to directly obtain rubbers with the rheological properties of the standard compounded product. Another important quality specification for polychloroprene is resistance to aging. In general, viscosity tends to increase upon storage. This phenomenon due to reticulation, which is more or less rapid depending on the operating conditions, is known under the term polymer aging. The increase in viscosity may or may not be accompanied by gel formation, which may result in partial insolubilization of the polychloroprene in the adhesive formulation and may also lead to physical and rheological changes in the polymer. Significant changes in properties occur. Resin acids that may be present within the polymerization system are known to prevent latex aging. However, this resin acid, in a mixture of solvent and adhesive containing magnesia and phenolic resins, is responsible for the phenomenon of phase separation, which is observed after a more or less long elapsed time. One way to avoid this phenomenon is to polymerize chloroprene in the presence of small amounts of colophonium and modest amounts of fatty acids (French Patent No. 2164095). However, under these conditions, and especially if thiuram is added at the end of the polymerization, it is observed that the natural aging of the polychloroprene increases. One of the conventional techniques making it possible to obtain polychloroprene in sol form consists of polymerizing chloroprene in the presence of a chain transfer agent. The resulting viscosity depends on the type and proportion of the chain transfer agent, as well as on the conversion of monomer to polymer. For economic reasons, it is desirable that the conversion rate be as high as possible;
It is desirable to exceed 70%. Introduced all at once at the start of polymerization, n
-By using only a small proportion of dodecyl mercaptan (n.DDM), polychloroprene with high viscosity can be obtained. However, the resulting polymers exhibit a partially reticulated structure in the form of a ``gel'' phase, which allows the polymer to partially dissolve in a suitable solvent. Becomes insoluble. Gels appear more quickly the higher the final conversion. A method well known in emulsion polymerization technology for reducing the average molecular weight of a polymer at a given conversion is the addition of modifiers intermittently or continuously over the entire period of polymerization. consists of doing. An improvement to this general method was published in a German patent
Proposed in issue PS2060659. However, this technique does not allow the complete absence of gels in the polychloroprene latex, which has a high viscosity as a solution;
Especially after latex aging and conversion rate is about 70%
This is true when exceeding the High viscosity in this description refers to high viscosity in toluene.
The Bruckfield viscosity of a 10% solution measured at 23°C is at least about 2500 mPa.s. The main object of the present invention is to provide a process for producing polychloroprene that allows the viscosity of the polymer to be adjusted over a wide range without forming gels while carrying out the polymerization to commercially acceptable conversion rates. purpose. Another intended object of the present invention is to obtain a high viscosity chloroprene "sol" that is free of gels or reticulated long chains that could lead to their formation. The invention further provides polychloroprenes for use in mixtures of solvents and adhesives, which have high viscosity, good natural aging properties, improved rheological behavior and do not lead to phase separation phenomena. purpose. According to the present invention, by combining the effects of two chain transfer agents with different reactivities, when the conversion rate of monomer to polymer is the same, the conventional chain transfer agent using only one chain transfer agent can be used. It has been found that it is possible to obtain polymers with high viscosity in solution, with improved rheological behavior compared to techniques, without the formation of gels. The activity of a chain transfer agent can be measured by its reaction rate relative to the polymerization rate of the monomer or monomers to be polymerized. According to the invention, the process consists of polymerizing chloroprene or a mixture of chloroprene with up to 20% by weight of copolymerizable monomers in an alkaline aqueous emulsion in the presence of a chain transfer agent; A chain transfer agent whose relative reaction rate is greater than that of chloroprene is added at the beginning, and then a chain transfer agent whose relative reaction rate is substantially equal to that of chloroprene is added intermittently or continuously during the reaction. It is characterized by As a result of the combination of these two transfer agents according to the invention, the formation of substances that have too high a molecular weight and are therefore too branched is prevented over the entire period of the polymerization.
Such results cannot be achieved by using only one transfer agent according to conventional techniques. Chain transfer agents that can be used according to the invention generally include:
It may be selected from among the molecular weight modifiers known in the chloroprene polymerization art after determining their reactivity. Among transfer agents, hereinafter referred to as X-transfer agents, which exhibit a higher relative reaction rate than that of chloroprene, those having the formula R-CI ₃ (where R represents hydrogen or an alkyl group having 1 to 3 carbon atoms) )
Particular mention may be made of the compounds. Particularly preferred is iodofluorum. Transfer agents, hereinafter referred to as Y-transfer agents, exhibiting a relative reaction rate substantially equal to that of chloroprene include n-octyl mercaptan, n-
Mention may especially be made of straight-chain or branched aliphatic mercaptans having 8 to 18 carbon atoms, such as dodecyl mercaptan, isododecyl mercaptan. Due to its commercial availability, n-
Dodecyl mercaptan is particularly utilized. Similarly, aromatic disulfides such as benzanilide disulfide can also be utilized. The transfer agents X and Y can be introduced into the reaction medium in the form of a solution, emulsion or in pure form. The conversion of one or several monomers, the amount of chain transfer agent, and the polymerization temperature are polymerization variables in the process of the invention. The amount of transfer agent X added at the beginning of the polymerization is from 50 to 700 ppm, expressed as the weight of iodoform relative to the weight of chloroprene charged. The total amount of transfer agent Y is a function of chloroprene conversion and polymerization temperature. Generally, this amount is n-dodecyl mercaptan (n.
DDM) may be 10 to 70 ppm by weight. The polymerization temperature θ is 5 to 50°C. Within this range, and assuming that the proportions of X-0.0014Xθ It may be advantageous to introduce the transfer agent Y while varying the rate of introduction, and generally increasing the rate of introduction. The manner in which the rate of introduction increases as a function of monomer conversion may be linear or non-linear starting from a certain monomer conversion so as to change the molecular weight distribution of the polymer. . In this case, the total amount of Y may be from 10 to 300 ppm, expressed by weight of n-DDM, per 1% conversion of monomer. When using transfer agents X and Y other than iodoform and n-DDM, their amounts are calculated by a simple ratio of molecular weights. Transfer agent Y may be added intermittently or continuously. Whatever the method used, care must be taken that the amount introduced does not violate the limits set out above as a function of conversion. By doing so, the final conversion of monomer to polymer can reach 90% at low polymerization temperatures and 80% at higher temperatures. In a modification of this method, a transfer agent having a relative reaction rate higher than that of chloroprene can be added to the transfer agent Y during the reaction, preferably after the conversion of chloroprene has reached 50%. .
This transfer agent may be the same or different from the transfer agent introduced at the beginning of the polymerization. Apart from the improvements according to the invention, the polymerization is carried out by current technology for the polymerization of chloroprene in alkaline emulsions in the presence of chain transfer agents. Chloroprene may be copolymerized with other monomers having at least one ethylene double bond. As a monomer that can be copolymerized with chloroprene,
Vinyl aromatics such as styrene, vinyltoluene and vinylnaphthalene, acrylic methacrylic acids such as ethyl acrylate, methyl acrylate and acrylonitrile and also their esters and nitrile derivatives, 1,3-butadiene, isoprene, 1-chlorobutadiene, 2,
Mention may be made of aliphatic conjugated diolefins such as 3-dichlorobutadiene and 2,3-dimethylbutadiene, vinyl ethers and ketones such as methyl vinyl ether, vinyl acetate and methyl vinyl ketone. Polymerization is carried out in aqueous emulsion using standard catalysts that generate free radicals. Mention may in particular be made of peroxide compounds such as alkali metal or ammonium persulfates, aqueous hydrogen peroxide, cumene peroxide, benzoyl peroxide, and also alkali metal and ammonium ferricyanides. The concentration of monomers present in the aqueous emulsion is not critical and is generally 30 to 60% of the total weight of the emulsion.
is within the range of Polymerization is carried out in an inert atmosphere in the absence of oxygen. The pH of the emulsion is between 11 and 13. Any conventional emulsifier and protective colloid can be used to create the chloroprene emulsion. These agents include salts soluble in water, especially collofonium or collofonium derivatives of long-chain fatty acids, pine resin, wood, tall oil;
Partially polymerized, isomerized or dismutated sodium, potassium or ammonium salts of corofan; sulfates, alkyl sulfates and alkyl sulfonates of fatty alcohols; alkylaryl sulfonic acids Mention may also be made of the alkali salts of formalin with arylsulfonic acids, such as naphthalenesulfonic acid, and of ethylene oxide and phenol. For the production of polychloroprene using adhesives with solvents, emulsifier systems with a weight composition of 1.8 to 3% of resin derivatives and 0.1 to 1% of saturated or unsaturated fatty acids relative to chloroprene are particularly preferred (as described in French patent no. 2164095 and U.S. Patent No. 3872043). Polymerization can be stopped at any time by addition of conventional polymerization inhibitors and the conversion should be as high as possible, preferably at least 70%. Upon termination of polymerization, di-tert-butyl para-cresol, 2,2'-methylenebis(6-tert-butyl-para-cresol), 2,2'-thiobis(4,
Conventional antioxidant compounds such as 6-di-tert-butylphenol), 2,6-di-tert-butyl-4-phenylphenol can be incorporated into the latex as well. Polychloroprene may be isolated from the latex by any known method, such as by condensation in a cryostat or steam-heated bath, washing and drying. The process of the invention makes it possible to obtain polychloroprene in sol form with high conversions and with strong cohesive forces and exceptionally satisfactory rheological behavior. This polychloroprene has good resistance to aging even in the absence of antiaging agents. This polychloroprene is particularly suitable for use as a base polymer for the production of glues and adhesives without the need for prior mastication. The invention will be further illustrated by the following examples, but the invention is not limited thereto. Example 1 In the polymerization tank: - 100 parts by weight of chloroprene - 100 parts by weight of water - Resin acid: 2 parts by weight of polymorphonium (phe'dre V, registered trademark of Passicos) - Sodium oleate 0.4 - Soda (100%) 0.46 - Sodium salt of methylene-bis-alkylene-naphthalenesulfonic acid
Distabex LS, a registered trademark of Fransaise des Matie'res Colorantes
0.875 parts by weight - Iodoform 0.0275 〃 A Ferrous sulfate (7H ₂ O) 0.00384 parts by weight Disodium salt of ethylenediaminetetraacetic acid [Masouol B, registered trademark of PROTEX]
0.00577 〃 Soda 0.00124 〃 Water 1.026 〃 B Sodium dithionite 0.0294 〃 Water 0.588 〃 Together with the starting catalyst. Polymerization is carried out for 10 hours at +10° C. by appropriately adjusting the flow rate of the aqueous solution of ammonium persulfate. Immediately after the start of the polymerization, 20 ppm of n-dodecylmercapotan per 1% conversion of monomer to polymer is continuously added. The polymerization is stopped at a conversion of 80% by a mixture of: - 0.8 parts by weight of chloroprene - 0.02 parts by weight of sodium lauryl sulfate - 0.01 parts of phenothiazine - 2.93 parts of water Finally, ditertiary dissolved in chloroprene (2.93 parts) Add 0.4 parts of butyl para-cresol into the latex. Entrainment of the latex with water vapor and isolation is carried out by methods customary for polychloroprene. In particular, isolation is carried out by coagulating a latex with a pH of 6.5 in a -20°C cold bath. The resulting film is washed and dried. The resulting polychloroprene is measured for viscosity, rheological behavior and the presence of gels. Viscosity: Brutzfield viscometer model LVT
Rheological behavior of a 10% by weight solution in toluene at 23°C: Determination of the Weissenberg effect [Nature, March 1, 1947, Vol. 159, 310-311
A continuum theory of rheological phenomena by K. Weissenberg, Page.
rheological phenomena) Polychloroprene is dissolved in toluene to obtain a viscosity of 5000 mPa.s. A cylindrical rod with a millimeter scale and a conical end is immersed in the liquid so that the liquid level is at "0" on the scale. When the rod rotates at 300 revolutions per minute,
A viscoelastic liquid rises along the rod. The height raised in millimeters after 30 seconds of rotation is called the "Weissenberg rise" and is proportional to the force perpendicular to the applied shear stress (normal force). Test temperature: 23° C. The Weissenberg rise characterizes the elasticity and brossabilite tendency of the polymer solution; the weaker this tendency is, the better the rheological behavior is. Presence of Gel 50 mg of polychloroprene are dissolved in tetrahydrofuran with stirring for 2 hours using a vibratory stirrer. Filter the solution on a 0.45μ Teflon filter. If the solution passes completely through the filter, the polychloroprene is considered gel-free (-). The polychloroprene obtained in this example is
It exhibits a viscosity of 4500 mPa.s and a Weissenberg effect of 40 mm. No gel was observed initially and no gel was observed after aging at 70°C for 3 days. Examples 2 to 16 Polymerizations are carried out in the same manner as in Example 1, varying the polymerization temperature, the amounts of iodoform and n-dodecylmercaptan. The proportion of iodoform is expressed in parts by weight of iodoform relative to the weight of chloroprene charged. The proportion of n-DDM is expressed in parts by weight of n-dodecylmercaptan relative to the weight of chloroprene, per 1% conversion. The results are shown in Table 1. Comparative Examples A to G Polymerizations are carried out as in Example 1 without using iodoform and instead introducing various amounts of n-DDM into the initial charge. In these examples, no additional n-DDM is added during the reaction. Polymerization is stopped when the conversion reaches 80%. The results are shown in Table 2. For viscosities equal to or greater than 1100 mPa.s, the presence of a small amount of gel in the initial polymer (+);
Poor aging properties of the polymer and high Weissenberg effect are observed. Comparative Examples H to N The polymerization of Example 1 is carried out, but the iodoform is replaced with different amounts of n-DDM, and different amounts of n-DDM are added continuously during the polymerization. Conversion rate
Stop polymerization when reaching 80%. The results are shown in Table 3. When the initial n-DDM rate is low, an improvement is observed compared to tests A to G. However, when the viscosity is approximately 2000 mPa.s (Test J), gels form rapidly upon aging. Example 17 The polymerization is carried out as in Example 1, but the proportion of n-DDM is varied as a function of monomer as shown below:

[Table] Polymerization is stopped at a conversion rate of 80%. The resulting polychloroprene exhibits a viscosity of 800 mPa.s (10% solution in toluene) and a Weissenberg effect of 10 mm. Both the pristine polymer and the polymer aged for 3 days at 70°C are gel-free. Example 18 Polymerization is carried out as in Example 1, except that the polymerization temperature is 30° C. and the initial iodoform is 0.0400 parts by weight. The proportion of n-DDM is varied as a function of conversion as follows:

[Table] Polymerization is stopped at a conversion rate of 80%. The viscosity of the resulting polychloroprene is 950mPa.s
and its Weissenberg effect is 25 mm. No gel is detected in either the initial polymer or the polymer after aging at 70° C. for 3 days. Example 19 Polymerization is carried out as in Example 1 at 10°C. The amount of iodoform initially charged is 0.0250 parts by weight. After initiation of polymerization, n-DDM is then
and iodoform are added continuously according to the method shown below:

【table】 Polymerization is stopped at a conversion rate of 85%. Viscosity of polychloroprene 670mPa.s Weissenberg effect 10 No gel

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Claims (1)

[Claims] 1. At the initiation of polymerization, a chain transfer agent X whose relative reaction rate is higher than that of chloroprene is added, and then a chain transfer agent Y whose relative reaction rate is substantially equal to that of chloroprene is added. polymerizable in alkaline aqueous emulsions of chloroprene and with chloroprene in the presence of emulsifiers and chain transfer agents, characterized in that chloroprene is added intermittently or continuously during the reaction, up to 20% by weight. Polymerization method of mixtures with monomers. 2. The method of item 1 above, characterized in that the transfer agent X is a compound of the formula R- _CI3 , where R represents hydrogen or a _C1 - _C3 alkyl group. 3. The method of item 2 above, wherein the transfer agent is iodoform. 4. Any one of the above items 1 to 3, wherein the transfer agent Y is selected from the group consisting of linear or branched alkyl mercaptans having 8 to 18 carbon atoms and aromatic disulfides. the method of. 5. The method of item 4 above, wherein the transfer agent is n-dodecylmercaptan. 6. The method of item 4 above, wherein the transfer agent is benzanilide disulfide. 7. The method according to any one of items 1 to 6 above, wherein the polymerization temperature θ is 5 to 50°C. 8 The amount of transfer agent
700 ppm and the rate of introduction of transfer agent Y is constant, the amount of transfer agent Y per 1% conversion of monomer to polymer is the amount of n-dodecyl mercaptan relative to the weight of chloroprene charged. 8. The method according to any one of items 1 to 7 above, characterized in that the content is 10 to 70 ppm expressed by weight. 9 The amount of transfer agent
700 ppm, and the rate of introduction of transfer agent Y increases, assuming that the amount of transfer agent per 1% conversion of monomer to polymer, expressed as the weight of n-dodecylmercaptan relative to the chloroprene charged, is The first above, characterized in that the concentration is 10 to 300 ppm.
- Any method of Section 7. 10. The method according to any one of items 1 to 9 above, characterized in that, in addition to transfer agent Y, a transfer agent having a relative reaction rate higher than that of chloroprene is introduced during polymerization. 11. The method according to any one of items 1 to 8 above, wherein the minimum value of the total amount of transfer agent is calculated by the formula: Y (ppm/conversion percentage) > 14 + 1.9 θ - 0.08X - 0.0014X θ. 12 Emulsifier system is 1.8 to 3 for chloroprene
The above-mentioned first to first compositions are characterized in that they contain 0.1 to 1% by weight of a saturated and/or unsaturated fatty acid or an alkali salt thereof.
Either method in Section 1.